1993 175Hp 2/S Yamaha alarm buzzer with no indication

[Ebit]

Hi I have a 1993 Yamaha 175 HP 2-stroke motor (BETO NZ model) which has developed an irritating problem.

The alarm buzzer goes off after about 2-3 minutes of running at around 4000-4500 rpm (upper revs).
Unfortunately the standard multifunction LCD displays (MFD) dont show any cause, not even a fleeting apparance.
(On starting the LCD display passes its self-test)

As one would expect, once the alarm buzzer sounds the motor revs are automatically cut.
I always throttle back to about 1200 and wait for the buzzer to stop by itself.

Each time this happens the buzzer consistently sounds for approx 38 seconds, (probably a programmed timed period regardless of issue?). Once the buzzer has stopped I can throttle up again and get another 2-3 minutes at the 4-4k5 rpm end.

If I run at lower revs say 3600 I usually dont get any buzzer action and all is fine.

So the first problem is:-
The motor protection circuits are activated as evidenced by the cutting of revs but the MFD doesnt show the cause.
A protection sensor that is wired to slow the motor in this built-in controlled fashion surely should be displayed but it isnt in my case.

Oil levels in the upper and lower tanks are all fine, the top-up proceedure works fine besides the level alarms would show up on the display,

The temp warning indicator on the MFD doesnt activate and the tail tail water stream is strong although I understanmd the take-off for this is prior to the cooling water heading through the head.

While there is no 'engine overreving' alarm indicator the motor can run up to about 5500 flat out. 4500 is just faster criusing (~35knts)

I want to take a methodical process of ellimination approach so any considered ideas would be welcome.

Thanks
E

 

[Capt Ken]

Re: 1993 175Hp 2/S Yamaha alarm buzzer with no indication

Next time it does this, remove the cowling and unplug the brown wire at the top of each head. When the buzzer quits, it will tell you which head is over heating. If its the starboard head, it's a water volume problem.

 

[Ebit]

Re: 1993 175Hp 2/S Yamaha alarm buzzer with no indication

Thanks Capt Ken. I'll prepare to do as you suggest though I'll need to run with the cowl off from the start as the buzzer will only be on for the 38 seconds which is not long when you have to slow to a stop and pull the massive hood off in the wake!

Why do you think the over temperature alarm indicator is not coming up if the motor is over heating? The meters self test shows the indicator is okay.

E

 

[Capt Ken]

Re: 1993 175Hp 2/S Yamaha alarm buzzer with no indication

Self test doesn't always mean everything works. Three things will trigger the alarm. Temp, low oil or bad battery connection

 

[Ebit]

Re: 1993 175Hp 2/S Yamaha alarm buzzer with no indication

I see. No 'over-reving' alarm? There's no indicator for that anyway.
The only battery is the start battery and the motor starts fine making me think that the connection is good.
So we're heading for over-temperature or oil issues.
I have heard of incorrect oil causing over heating but the oil I've been using for years and years is a Shell product for 2-strokes called (here in NZ anyway) 'Nautalus'.

I'll go recce the "brown wires"!!

 

[Ebit]

Re: 1993 175Hp 2/S Yamaha alarm buzzer with no indication

I had a play with the engine today. I located the two thermistors one on each head and with the ignition on, checked both of the circuits by shorting what turns out to be the pink wire (sheathed in brown) to ground. The buzzer sounded for as long as the wire was grounded suggesting that my 38seconds as originally reported was an actual cool down period. So with the buzzer going the multifunction display did not show over temperature so now I know two things,
1. My problem probably is genuine overheating, probably through salt build-up in the jackets and
2. The over temp alarm on the multifunction display is not working despite a successful self-test on first power up.
So Capt Ken apart from the wire colour, you're bang on. Keep it coming.
Next task I performed was to inspect the back of the multifunction display. The MFD in question has speedo, fuel level and the 3 alarm displays, temp,batt and low fuel. I see the fuel gauge wiring going in and a red and black and yellow wires going in plus backlighting power. The display doesn't power up if either the red, black or yellow are individually disconnected so i figure they're crucial to basic operation.
But to my surprise I see two other wires which are unterminated and these are white and grey. I suspect that the over temp and bad battery voltage alarms are not even connected and have been this way since installed on the boat in April 1993!!!
The trouble now is I can not see any unterminated cores in the looms that come from the motor which look remotely like they are the missing signal wires.
Has anybody got any ideas on this. At least this is progress. I don't have a detailed circuit diagram so can't work this out for myself.
Cheers